1. Field of the Invention
The invention relates to an encoder, a decoder, an encoding method and a decoding method.
2. Description of the Related technology
Generally speaking, lossless image compression technological trends may be classified into two kinds. The first kind of lossless image compression technology, such as JPEG-LS, H.264-LS, AIC or DPCM-H.264-LS, does not include the frequency transform and quantization. The second kind of lossless image compression technology, such as JPEG2000-LS or HD photo, includes the frequency transform and quantization, and may be applied to the lossy and lossless image compression technologies simultaneously.
The lossless image compression technology widely used in the digital archive and the medical image includes JPEG-LS and JPEG2000-LS, which are too old. Although the compression performance of JPEG-LS is far higher than that of JPEG2000-LS, JPEG-LS cannot be simultaneously applied to the lossy image compression in the same encoder. In addition, the application popularization of JPEG2000 is extremely low. Compared with the lossless compression performance, the compression efficiency of JPEG2000-LS and H.264-LS is far lower than that of DPCM-based H.264-LS. However, DPCM-based H.264-LS cannot be applied to the lossy image compression technology. Although the lossless image compression technology is added to the newest H.264 lossy image compression technology, the performance of the added lossless image compression technology is relatively lower than that of each of JPEG-LS and JPEG2000-LS. Although Microsoft has published the image compression technology HD Photo capable of supporting the lossy and lossless conditions, the compression ratio of the lossless image is also far lower than that of each of JPEG-LS and JPEG2000-LS.
Therefore, it is an important issue in the current image compression to provide the universal encoding technology having the high compression performance and capable of supporting the lossy and lossless conditions simultaneously.